Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$169.90	9.488%	$186.0201	$186.02	$186.00	$186.00
Purchase #2	$90.41	11.394%	$100.7113	$100.71	$100.70	$100.70
Purchase #3	$14.46	8.538%	$15.6946	$15.69	$15.70	$15.70
Purchase #4	$43.61	6.852%	$46.5982	$46.60	$46.60	$46.60
Purchase #5	$45.74	10.829%	$50.6932	$50.69	$50.70	$50.70
Purchase #6	$104.82	4.325%	$109.3535	$109.35	$109.35	$109.40
Purchase #7	$220.84	13.410%	$250.4546	$250.45	$250.45	$250.50
7 purchase totals =	$689.78		$759.5255	$759.51	$759.50	$759.60